1. Field of the Invention
The present invention generally relates to a woven fabric for use in a paper, cellulose or board manufacturing machine that is seamed by interlocking loops along each of two fabric edges to form an endless woven fabric.
2. Description of the Prior Art
As will be known to those skilled in the art, papermaking machines generally include three sections which are referred to as the forming, press and dryer sections. A felt is generally employed to transport the formed, wet sheet through the press and dryer sections of the papermaking equipment. The felt must be particularly adapted to specific conditions encountered in papermaking.
Typically, such felts include a supporting base, such as a woven fabric, and a paper carrying or supporting layer fixed to the base. The paper carrying or supporting layer is generally softer and smoother than the base layer. The support layer is often a non-woven batt material which has been affixed to the base and has homogeneous characteristics as to permeability, compaction and drainage. Slight irregularities or imperfections in the support layer are undesirable in virtually all papermaking operations. Inconsistencies in the felt thickness, gauge or weight can cause undesirable vibrations during operation of the equipment.
In press fabrics, the batt material is often anchored to a base fabric which is provided with end loops to join the fabric. Many of these fabrics are woven as endless loops in patterns that provide the seaming loops at each end of the fabric. Standard woven loop base constructions frequently include two layers of weft yarns in a low density, symmetrical construction. However, these base fabrics typically provide limited batt anchorage and sheet support due to low surface contact area. This necessitates the use of a third, topical laminate structure, having a higher density of weft or warp yarns. The laminate is generally bound to the primary base by means of filament entanglement during a post weaving needling process. This process can be costly and time consuming.
Another problem associated with endlessly woven seamed fabrics is seaming of the fabric. Standard endlessly woven loop seam products are made with stacked weft pairs, formed by looping around a forming monofilament. A common problem associated with this type of loop formation is non-uniform loop alignment, both in the vertical and horizontal axis, when the forming wire is removed. This misalignment creates a seam that is difficult to mesh.
FIGS. 1-3 show representative loop misalignments experienced in common prior art endlessly woven seams. Generally, as a loom weaves the loops in an endless weave construction, it naturally offsets the returning weft position slightly from its outgoing weft position. It is possible to maintain the weft yarns in a stacked relationship throughout the fabric through the balanced weave of the warp yarns. However, the last warp yarn 2 does not have a balancing yarn on one of its sides and, therefore, an unbalanced crimp force is applied to the weft yarns in the loop area, as shown by the arrows in FIG. 2. As a result, the two weft yarn passes which form each loop are not balanced by warps and the loops tend to be misaligned.
A similar misalignment of the loops occurs in flat woven fabrics wherein the tie back portion of the warp yarn is offset from the outgoing portion of the warp yarn during loop formation.
The present invention combines two high density structures during the weaving process, with the primary base construction being used to form endless type seam loops. This is achieved by means of unique weave patterns that stitch in a higher density weft layer of yarns to provide greater batt anchorage and maintain a stacked weft arrangement in the base for uniform, vertically aligned, loop formation.